1. Field of the Invention
The present invention relates to an organic EL panel (organic electroluminescence panel) and a method of manufacturing the same.
2. Description of the Prior Art
A method of manufacturing an inorganic EL panel disclosed in Japanese Unexamined Patent Publication No. 5-108014 will be described as a conventional example. According to this example, as shown in FIG. 1, a mask 18 having a window pattern corresponding to the emission film portions for pixels of a display color is disposed near a panel substrate 1 on which a transparent electrode film 2 and an insulating film 16 are formed. In this state, emission layers 17 of the same display color are selectively formed simultaneously at positions of the window pattern by vacuum deposition. Hence, emission portions of different display colors are sequentially formed at different positions in units of colors.
Japanese Unexamined Patent Publication No. 7-121056 discloses a method of manufacturing the color filter of a plasma display or liquid crystal display. According to this method, a substrate formed with a photosensitive body layer having an organic photoconductive layer is charged to desired polarity, and is selectively exposed to form a latent image. Then, toner is attached to this substrate to form a pattern. This substrate is calcined to remove the organic photoconductive layer, thereby obtaining a desired pattern.
As a method of manufacturing the color filter of a liquid crystal display, a pigment dispersing method utilizing photolithography is also known. According to this method, a substrate is coated with a photoconductive polymer dispersed with a color pigment, and is exposed through a photomask. After that, this substrate is developed and etched to form a color pattern. This method is repeated for each of red, green, and blue.
With the above method of sliding the mask in accordance with the colors, the substrate deforms or deflects due to the weight of the mask or thermal expansion caused by radiation heat during deposition, and fine positional control of the mask is difficult to perform. Therefore, the layers overlap each other and insufficient separation occurs easily. Also, it is difficult to form a large-size screen. To obtain a mask, a pattern is formed in a thin metal plate by photoetching. The finer the pattern is, the more easily the pattern is disconnected, making it difficult to fabricate the mask itself. In order to prevent short-circuiting of the respective pixels, the mask and the substrate must be separated from each other. However, the deposition material rounds about during deposition, and accordingly further shrinkage in device geometries is limited.
Since an organic EL panel uses an organic material having no heat resistance as the material of an emission layer, a hole transport layer, and the like, it cannot employ the method of which uses a photosensitive body and develops toner dispersed with an inorganic pigment and calcines the toner to remove the photosensitive body. Since a white electroluminescent material is not currently available for an organic EL panel, it is difficult to utilize a color filter.
Assume that the pigment dispersing method is applied to a color organic EL panel. In this case, the organic EL panel which is very weak against water utilizes a wet process for patterning wherein a photosensitive polymer is applied to the substrate, is exposed through a photomask, and is developed and etched. Accordingly, generation and growth of a dark spot, and generation of a pixel defect due to separation of an organic layer-cathode interface, readily occur.